1. Field of the Disclosure
This disclosure relates to processes for forming electronic devices, and more particularly to, processes for forming electronic devices including polishing metal-containing layers.
2. Description of the Related Art
Polishing metal-containing layers in electronic devices, and particularly integrated circuits, can be difficult due to predictable and unpredictable complications, even when only mechanical parameters are changed. Many contact or via plug and interconnect schemes include titanium nitride as a barrier layer. In many electronic devices, contact or via plugs include tungsten, and interconnects include copper. Because tungsten and titanium are both refractory metal elements, the tungsten and titanium nitride can be polished using the same polishing pad and the same polishing slurry. Copper polishes differently from refractory metals. Thus, a polishing process that is tailored for polishing tungsten is not well suited for polishing copper.
FIGS. 1 and 2 illustrate that different polishing pads, different polishing slurries, or any combination thereof are used when polishing conductive layers in which copper overlies titanium nitride. FIG. 1 includes an illustration of a cross-sectional view of a portion of a workpiece 10 that includes an insulating layer 102 and a contact or via plug 104 that extends through the insulating layer 102. A patterned insulating layer 122 overlies the insulating layer 102 and includes an interconnect trench. A plurality of conductive layers overlie the patterned insulating layer 122 and lie within the interconnect trench. The conductive layers include a titanium nitride layer 144, a copper seed layer 146, and a plated copper layer 148.
FIG. 1 illustrates the workpiece 10 as the plated copper layer 148 is being polished using a polishing pad 166 and a polishing slurry 16 that includes a liquid medium 162 and abrasive particles 164. The polishing pad 166 and polishing slurry 16 are tailored for polishing copper within the copper seed layer 146 and the plated copper layer 148. The combination of the polishing pad 166 and polishing slurry 16 does a poor job at polishing the titanium nitride layer 144. Thus, a different polishing pad or a different slurry is used to remove the titanium nitride layer 144.
FIG. 2 illustrates the workpiece 10 as the titanium nitride layer 144 is being polished using a polishing pad 266 and a polishing slurry 26 that includes a liquid medium 262 and abrasive particles 264. The polishing pad 266 and polishing slurry 26 are tailored for polishing the titanium nitride layer 144. The polishing pad 266, the liquid medium 262, the abrasive particles 264, another part of the polishing slurry 26, or any combination thereof is different from its corresponding item as illustrated in FIG. 1 (e.g., the polishing slurry 26 is different from the polishing slurry 16). The workpiece 10 may need to be moved from one polishing platen to a different polishing platen to remove the conductive layers lying outside the interconnect trench. Thus, the polishing process is discontinuous because a different polishing pad or a different polishing slurry causes a significant delay between the time the copper polishing is completed and the titanium nitride polishing begins. This delay affects the equipment throughput, the polishing sequence may require special handling (e.g., keep the workpiece wet so that abrasive particles do not dry onto the surface of the workpiece 10), may cause another complicating factor, or any combination thereof.
Therefore, skilled artisans have had to choose between using (1) the same polishing pad and polishing slurry that works well for one material (e.g., copper) and not another (e.g., titanium nitride) or (2) use different polishing pads, different polishing slurries, or any combination thereof, wherein each polishing pad, each polishing slurry, or each combination of polishing pad and polishing slurry is tailored to remove a particular material, but not all materials, within the plurality of conductive layers that form an interconnect.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the invention.